The　development　of　solid-state　electrolytes　for　Li-metal　batteries　demands　high　ionic　conductivity,　interfacial　compatibility,　and　robust　mechanical　strength　to　address　lithium　dendrite　formation　and　manufacturing　challenges.　Herein,　We　report　a　high-performance　SSE,　designed　via　in-situ　polymerization　of　cross-linked　poly(vinyl　carbonate)　(PVC)　on　a　LATSP-coated　polypropylene　(PP)　separator,　resulting　a　LATSP@PP-PVC　composite　solid　electrolyte.　The　PP　separator　ensures　mechanical　strength,　while　the　LATSP　coating　improves　wettability　and　lithium　salt　dissociation.　Additionally,　the　cross-linked　PVC　network　restricts　TFSI−　ion　migration,　enhancing　Li+　conductivity.　As　a　result,　the　composite　exhibits　excellent　mechanical　properties　(70　MPa　tensile　strength,　54　%　tensile　strain),　alongside　a　room-temperature　ionic　conductivity　(3.19　×　10−4　S　cm−1)　and　a　Li+　transference　number　of　0.468.　Li　metal　batteries　employing　this　SSE　paired　with　LiFePO4　cathodes　show　81.56　%　capacity　retention　after　800　cycles　at　2　C,　demonstrating　its　potential　for　commercial　solid-state　batteries.　These　findings　hold　promise　for　advancing　the　commercialization　of　composite　electrolytes　for　solid　state　batteries.　©　2025